Morphological and chemical study of the initial growth of CdS thin films deposited using an ammonia-free chemical process

We study the initial growth stages of CdS thin films deposited by an ammonia-free chemical bath deposition process. This ammonia-free process is more environmentally benign because it reduces potential ammonia release to the environment due to its high volatility. Instead of ammonia, sodium citrate was used as the complexing agent. We used atomic force microscopy (AFM), Rutherford backscattering (RBS) and X-ray photoelectron spectroscopy (XPS) to investigate the morphological and chemical modifications at the substrate surface during the first initial stages of the CdS deposition process. Additionally, X-ray diffraction (XRD) and optical transmission spectroscopy measurements were carried out to compliment the study. XPS results show that the first nucleation centers are composed by Cd(OH)₂ which agglomerate in patterns of bands, as demonstrated by AFM results. It is also observed that the conversion to CdS (by anionic exchange) of the first nucleus begins before the substrate surface is completely covered by a homogenous film.     

Highly Stable Aqueous Zinc‐Ion Storage Using a Layered Calcium Vanadium Oxide Bronze Cathode

Cost‐effective aqueous rechargeable batteries are attractive alternatives to non‐aqueous cells for stationary grid energy storage. Among different aqueous cells, zinc‐ion batteries (ZIBs), based on Zn²⁺ intercalation chemistry, stand out as they can employ high‐capacity Zn metal as the anode material. Herein, we report a layered calcium vanadium oxide bronze as the cathode material for aqueous Zn batteries. For the storage of the Zn²⁺ ions in the aqueous electrolyte, we demonstrate that the calcium‐based bronze structure can deliver a high capacity of 340 mA h g^?1 at 0.2 C, good rate capability, and very long cycling life (96 % retention after 3000 cycles at 80 C). Further, we investigate the Zn²⁺ storage mechanism, and the corresponding electrochemical kinetics in this bronze cathode. Finally, we show that our Zn cell delivers an energy density of 267 W h kg^?1 at a power density of 53.4 W kg^?1.     

Photochromism of tetrahydroindolizines. Part XIV: synthesis of cis-fixed conjugated photochromic pyridazinopyrrolo[1,2-b]isoquinolines incorporating carbon-rich linkers

New carbon-rich photochromic tetrahydroindolizines (THIs) bearing dihydroisoquinoline derivatives as heterocyclic bases (region B) have been synthesized via different chemical and photochemical pathways. Three alternative pathways for the synthesis of the target photochromic THI-based pyridazinopyrrolo[1,2-b]isoquinolines via in situ trapping with hydrazine hydrate have been established. In order to obtain high product yields, different Sonogashira-mediated coupling reactions have been optimized. Low temperature multichannel UV–vis and flash photolysis techniques were used to detect the photochromic and kinetic properties of the synthesized system.     

A Site-Selective Doping Strategy of Carbon Anodes with Remarkable K-Ion Storage Capacity

The limited potassium-ion intercalation capacity of graphite hampers development of potassium-ion batteries (PIB). Edge-nitrogen doping is an effective approach to enhance K-ion storage in carbonaceous materials. One shortcoming is the lack of precise control over producing the edge-nitrogen configuration. Here, a molecular-scale copolymer pyrolysis strategy is used to precisely control edge-nitrogen doping in carbonaceous materials. This process results in defect-rich, edge-nitrogen doped carbons (ENDC) with a high nitrogen-doping level (up to 10.5 at %) and a high edge-nitrogen ratio (87.6 %). The optimized ENDC exhibits a high reversible capacity of 423 mAh g⁻¹, a high initial Coulombic efficiency of 65 %, superior rate capability, and long cycle life (93.8 % retention after three months). This strategy can be extended to design other edge-heteroatom-rich carbons through pyrolysis of copolymers for efficient storage of various mobile ions.     

Interface characterization of nickel contacts to bulk bismuth tellurium selenide

Transmission electron microscopy (TEM) characterization of nickel contacts to bulk bismuth tellurium selenide [Bi₂(Te,Se)₃] is reported. Samples were prepared in a dual column focused ion beam/scanning electron microscope (FIB/SEM) system using a lift‐out technique, with ion beam energy and exposure times carefully optimized to minimize sample damage. Diffusion of Ni into Bi₂(Te,Se)₃ was observed and the formation of a nickel telluride (NiTe) interfacial region confirmed after heat treatment at 200 °C. Selected area diffraction patterns provided evidence of a modified bismuth telluride–like structure at the interface, identified by analytical electron microscopy to be composed of Ni and Bi₂(Te,Se)₃. Copyright © 2009 John Wiley & Sons, Ltd.     

A Site‐Selective Doping Strategy of Carbon Anodes with Remarkable K‐Ion Storage Capacity

The limited potassium‐ion intercalation capacity of graphite hampers development of potassium‐ion batteries (PIB). Edge‐nitrogen doping is an effective approach to enhance K‐ion storage in carbonaceous materials. One shortcoming is the lack of precise control over producing the edge‐nitrogen configuration. Here, a molecular‐scale copolymer pyrolysis strategy is used to precisely control edge‐nitrogen doping in carbonaceous materials. This process results in defect‐rich, edge‐nitrogen doped carbons (ENDC) with a high nitrogen‐doping level (up to 10.5 at %) and a high edge‐nitrogen ratio (87.6 %). The optimized ENDC exhibits a high reversible capacity of 423 mAh g^?1, a high initial Coulombic efficiency of 65 %, superior rate capability, and long cycle life (93.8 % retention after three months). This strategy can be extended to design other edge‐heteroatom‐rich carbons through pyrolysis of copolymers for efficient storage of various mobile ions.     

The free energy of a reaction coordinate at multiple constraints: a concise formulation

The free energy as a function of the reaction coordinate (rc) is the key quantity for the computation of equilibrium and kinetic quantities. When it is considered as the potential of mean force, the problem is the calculation of the mean force for given values of the rc. We reinvestigate the PMCF (potential of mean constraint force) method which applies a constraint to the rc to compute the mean force as the mean negative constraint force and a metric tensor correction. The latter allows for the constraint imposed to the rc and possible artefacts due to multiple constraints of other variables which for practical reasons are often used in numerical simulations. Two main results are obtained that are of theoretical and practical interest. First, the correction term is given a very concise and simple shape which facilitates its interpretation and evaluation. Secondly, a theorem describes various rcs and possible combinations with constraints that can be used without introducing any correction to the constraint force. The results facilitate the computation of free energy by molecular dynamics simulations.     

Tuning the Electrochemical Performance of Titanium Carbide MXene by Controllable In Situ Anodic Oxidation

MXenes are a class of two‐dimensional (2D) transition metal carbides, nitrides and carbonitrides that have shown promise for high‐rate pseudocapacitive energy storage. However, the effects that irreversible oxidation have on the surface chemistry and electrochemical properties of MXenes are still not understood. Here we report on a controlled anodic oxidation method which improves the rate performance of titanium carbide MXene (Ti₃C₂T_x, T_x refers to ‐F, =O, ‐Cl and ‐OH) electrodes in acidic electrolytes. The capacitance retention at 2000 mV s^?1 (with respect to the lowest scan rate of 5 mV s^?1) increases gradually from 38 % to 66 % by tuning the degree of anodic oxidation. At the same time, a loss in the redox behavior of Ti₃C₂T_x is evident at high anodic potentials after oxidation. Several analysis methods are employed to reveal changes in the structure and surface chemistry while simultaneously introducing defects, without compromising electrochemically active sites, are key factors for improving the rate performance of Ti₃C₂T_x. This study demonstrates improvement of the electrochemical performance of MXene electrodes by performing a controlled anodic oxidation.     

Non-Flammable Electrolyte Enables High-Voltage and Wide-Temperature Lithium-Ion Batteries with Fast Charging

Electrolyte design has become ever more important to enhance the performance of lithium-ion batteries (LIBs). However, the flammability issue and high reactivity of the conventional electrolytes remain a major problem, especially when the LIBs are operated at high voltage and extreme temperatures. Herein, we design a novel non-flammable fluorinated ester electrolyte that enables high cycling stability in wide-temperature variations (e.g., −50 °C–60 °C) and superior power capability (fast charge rates up to 5.0 C) for the graphite||LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) battery at high voltage (i.e., >4.3 V vs. Li/Li⁺). Moreover, this work sheds new light on the dynamic evolution and interaction among the Li⁺, solvent, and anion at the molecular level. By elucidating the fundamental relationship between the Li⁺ solvation structure and electrochemical performance, we can facilitate the development of high-safety and high-energy-density batteries operating in harsh conditions.